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Shallow-Marine Trace Fossils of the Pochico Formation, Southern Spain: Palaeoenvironmental and Palaeogeographic Implications at the Gondwanan and Peri-Gondwanan Realm

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Shallow-Marine Trace Fossils of the Pochico Formation, Southern Spain: Palaeoenvironmental and Palaeogeographic Implications at the Gondwanan and Peri-Gondwanan Realm Journal of Iberian Geology 40 (3) 2014: 539-555 http://dx.doi.org/10.5209/rev_JIGE.2014.v40.n3.44308 www.ucm.es /info/estratig/journal.htm ISSN (print): 1698-6180. ISSN (online): 1886-7995 Lower/Middle Ordovician (Arenigian) shallow-marine trace fossils of the Pochico Formation, southern Spain: palaeoenvironmental and palaeogeographic implications at the Gondwanan and peri-Gondwanan realm F.J. Rodríguez-Tovar1, M. Stachacz2, A. Uchman2, M. Reolid3 1Departamento de Estratigrafía y Paleontología, Facultad de Ciencias, Universidad de Granada, 18002 Granada, Spain 2Jagiellonian University, Institute of Geological Sciences, Oleandry Str. 2a, PL-30-063 Kraków, Poland 3Departamento de Geología, Universidad de Jaén, Campus Las Lagunillas sn, 23071 Jaén, Spain e-mail addresses: [email protected] (F.J.R.-T., corresponding author); [email protected] (M.S.), [email protected] (A.U.); [email protected] (M.R.) Received: 29 January 2014 / Accepted: 13 August 2014 / Available online: 30 October 2014 Abstract Nineteen ichnospecies belonging to thirteen ichnogenera (Archaeonassa, Catenichnus, Cochlichnus, Cruziana, Didymaulichnus, ?Di- plichnites, Gordia, Lingulichnus, Lockeia, cf. Monocraterion, Planolites, Ptychoplasma, and Rusophycus) occur in the Pochico Forma- tion (Arenigian) in the Aldeaquemada section, Sierra Morena, southern Spain, just above the Armorican Quartzite. They belong to the archetypal Cruziana ichnofacies, indicating a lower shoreface-upper offshore zone. The low degree of sediment reworking may be due to a high rate of sedimentation. The trace fossil assemblage, rich in large Cruziana, is typical of the Armorican Quartzite that developed on the margins of Gondwana and peri-Gondwanan microcontinents. The distribution of ichnofauna during the Early Ordovician was partly palaeogeographically controlled, although ichnological data from the literature point to paths of migration between Gondwana, Baltica and Laurentia. Differences between the ichnofauna of Gondwana and Baltica could be conditioned by facies (clastics in Gondwana and carbonates in Baltica) causing a taphonomic filter, because Cruziana requires diversified clastic deposits for preservation. The ichnofauna would also be influenced by trophic group amensalism between filter feeding and deposit feeding fauna, the former prevailing in Baltica and the latter in Gondwana. Keywords: Ichnofossils, Arenigian, clastic sediments, Gondwana, peri-Gondwana, Iberia Resumen Se presenta el análisis sedimentológico/icnológico de los materiales de la Formación Pochico (Arenigian) de la sección de Aldeaque- mada, Sierra Morena, Sur de España, provincia de Jaén, justo por encima la Cuarcita Armoricana. Se han reconocido diecinueve icnoes- pecies pertenecientes a trece icnogéneros (Archaeonassa, Catenichnus, Cochlichnus, Cruziana, Didymaulichnus, ?Diplichnites, Gordia, Lingulichnus, Lockeia, cf. Monocraterion, Planolites, Ptychoplasma, y Rusophycus). Las características icnológicas junto con los rasgos sedimentológicos permiten asignarlas a las icnofacies arquetípicas de Cruziana, comunes de las zonas de shoreface inferior a offshore supe- rior. El grado de bioturbación relativamente bajo puede estar relacionado con una alta tasa de depósito. La asociación registrada, dominada por grandes Cruziana, es típica de la Cuarcita Armoricana desarrollada en los márgenes de Gondwana y peri-Gondwana. La distribucción de icnofósiles del Ordovícico temprano posee, en gran medida, un control paleogeográfico, aunque datos icnológicos procedentes de la literatura indican la existencia de migraciones entre Gondwana, Baltica y Laurentia. Las diferencias entre las asociaciones de Gondwana y Báltica pueden estar asociadas a las diferentes facies, con el dominio de materiales clásticos en Gondwana y de carbonatados en Báltica, causando un filtro tafonómico ya que el potencial de conservación de Cruziana es mucho mayor en las facies clásticas heterolíticas. A estos factores habría que añadir las estrategias de alimentación asociadas, diferenciando entre filtradores y aquellos que se alimentan de las partículas existentes en el sedimento, los primeros podrían verse favorecidos en Báltica y los segundos en Gondwana. Palabras clave: Icnofósiles, Arenigiense, sedimentos clásticos, Gondwana, peri-Gondwana, Iberia 540 Rodríguez-Tovar et al. / Journal of Iberian Geology 40 (3) 2014: 539-555 1. Introduction village by the El Negrillo pool of the Guarrizas River (GPS co-ordinates: N38°23.150′; W003°22.474′; ±9 m). Additional Arenigian shallow-marine clastic sediments of Western Eu- material was observed in the surroundings, especially at the rope, North Africa, South America and some parts of North bottom of the valley near this site, where nearly horizontal America are characterized by abundant trace fossils, includ- beds offered other in situ occurrences (GPS co-ordinates: ing large Cruziana, an ichnogenus first described from such N38°23.136′; W003°22.332′; ±8 m). Both localities are with- deposits in Bolivia (ďOrbigny, 1842). Trace fossils of these in the Despeñaperros Natural Park. facies are largely associated with quartzitic sandstones, in The Lower/Middle Ordovician in the Aldeaquemada France and on the Iberian Peninsula largely attributed to the area comprises two lithostratigraphic units: the Armorican Armorican Quartzite (Grès Armoricain) (Gutiérrez-Marco et Quartzite Formation and the Pochico Formation (Fig. 1C). al., 2002). The Armorican Quartzite, dated mostly to Areni- The Armorican Quartzite in the Central Iberian Zone is up gian, was deposited in several disconnected basins supplied to 500 m thick and composed of white orthoquartzites. The from local sources (Torsvik and Cocks, 2011). The Armorican lower part of the Armorican Quartzite Formation is not out- Quartzite and associated deposits rich in quartzite sandstones cropping in the studied area, but its upper member, about 200 may be considered as a facies deposited in shallow seas in m thick, with beds ranging from 30 cm to 12 m, is identified the margin part of Gondwana and peri-Gondwanan micro- in the Aldeaquemada area and described by Rey and Hidalgo continents in the stage of rifting and early drift of Avalonia (2004) and Lillo et al. (in press). Top beds of this member (Gutiérrez-Alonso et al., 2007). This area was a southern- display wavy bedding, cross-stratification and the trace fossil most part of Gondwana and was situated near the South Pole Cruziana. during the Early Ordovician (e.g., Cocks and Torsvik, 2002). The Pochico Formation, around 200 m-thick in the studied Although a general ichnological characterization of the area, is made up of alternating quartzites, quartz sandstones, Armorican Quartzite is lacking to date, trace fossils are an sandy shales, siltstones and mudstones. Stratal stacking al- important feature of this facies. They have been described lows three members to be distinguished (Tamain, 1972). Ac- in several sections and areas on the Iberian Peninsula (e.g., cording to Gutiérrez-Marco et al. (2013), the Pochico Forma- Delgado, 1886a, b; Bouyx, 1966; Baldwin, 1975, 1977a, b, c; tion probably corresponds to the Dapingian sequence sensu Crimes and Marcos, 1976; Kolb and Wolf, 1979; Pickerill et lato in the southern part of the Central-Iberian Zone in Spain, al., 1984; Romano, 1991; Neto de Carvalho, 2006; Sá et al., being in this case the Middle Ordovician in age (Bergström et 2011) and in France (Rouault, 1850; Lebesconte, 1883, 1886; al., 2009). The Lower Member (Pochico Alternations Mem- Durand 1984, 1985a, b; Fortey and Owens, 1999). ber) is around 60 m thick and features a series of quartzite In this paper, we describe a trace fossil assemblage in one beds alternating with finer sediments, showing wavy-bed- section of the Armorican Quartzite facies, just on the transi- ding (Fig. 2A), horizontal lamination (Fig. 2D), wave ripple tion of the Armorican Quartzite sensu stricto, and overlying cross-lamination and locally low angle cross-stratification heterolithic facies of the Pochico Formation in the Aldeaque- (Fig. 2E). The Middle Member (Yellowish Pochico Sand- mada section (Cimbarra section in Rey and Hidalgo, 2004), stone Member) contains about 100 m thick sandy shales with Central Iberian Zone (Fig. 1). Its palaeoenvironment is inter- wavy-bedding and locally hummocky cross-stratification. A preted in the Gondwanan and peri-Gondwanan context. Con- few horizons show distinct cracks (Fig. 2F). In the Middle sidering that the Pochico Formation is ichnologically almost Member, lingulid horizons have been recorded and related unexplored, a discussion of the more general ichnological to short catastrophic events (Emig and Gutiérrez-Marco, features of this facies based on the literature serves to sup- 1997). The Upper Member or Pochico Quartzite Intercala- port our interpretation. Collected trace fossils are housed in tions Member (50 m thick) is characterized by numerous the Department of Stratigraphy and Palaeontology, Faculty of quartzite beds intercalated with finer clastics, similar to the Sciences, University of Granada (label Aq). first member. Most of these rocks are characterized by the low degree of sediment reworking and primary structures are 2. Geological setting usually clearly visible. This study is focused on sedimentological and ichnologi- During the Early Ordovician, the Iberian Massif formed cal features at the transition between the Armorican Quartzite part of the northwest margin of Gondwana (e.g., Von Raumer Formation and the Pochico Formation, where a 29 m-thick et al.,
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